Wavefront sensing is employed to determine the distorting wavefront caused by the turbulent atmosphere and one or more the following methods are generally employed to provide an estimate of the distorting wavefront.
1. Dithering. This method of wavefront sensing continuously changes the adaptive optics and monitors the image quality of the observed image. U.S. Pat. No. 3,979,585 entitled “Adaptive imaging telescope with camera-computer transform image quality sensing and electro-optic phase shifting” and the publication by M. A. Voronstov and V. P. Sivokon, entitled “Stochastic parallel-radiant-descent technique for high-resolution wave-front phase-distortion correction,” J. Opt. Soc. Am., A, 15,2745 (1988) are examples of this approach. They are sequential techniques, in the sense that a physical property of the adaptive optics is changed. and if the next (time-sequential) image is sharper the change is increased, otherwise the change is reversed. This is a physical search for “best focus” and is how the human eye and most cameras work.
2. Shearing Interferometer. This method of wavefront sensing uses a reference beam to create an interference pattern, from which the unknown wavefront is estimated. It requires a laser-based interferometer. U.S. Pat. No. 3,923,400 entitled “Real-time wavefront correction system” describes this approach.
3. Shack-Hartmann Sensor. This device employs an array of lenses to focus multiple, small images, each seen through a different section of the aperture, onto a detector. Shifts in the small images are caused by local tilts in the waveform, which allows the wavefront to be reconstructed. U.S. Pat. No. 4,141,652 entitled “Sensor system for detecting wavefront distortion in a return beam of light” and U.S. Pat. No. 5,350,911 entitled “Wavefront error estimation derived from observation of arbitrary unknown extended scenes” disclose the use a Shack-Hartmann sensor.
4. Curvature Sensing. This method is described in the publication by F. Roddier et al. entitled “A simple low-order adaptive optics system for near-infrared applications,” Publications of the Astronomical Society of the Pacific, 103,131 (1991), whereby two or more images are measured along the path of the optical system. The local curvature of the propagating wave is determined and it is propagated, by computer calculation, back to the aperture to form the wavefront estimate.
5. Phase diversity. This method employs diverse images, measured simultaneously whereby the diversity is a quadratic phase shift, which can be introduced by defocusing the optical system. Additional equipment in needed to record the out-of-focus image. U.S. Pat. No. 4,309,602 entitled “Wavefront sensing by phase retrieval”, U.S. Pat. No. 5,384,455 entitled “Measurement-diverse speckle imaging”, U.S. Pat. No. 5,610,707 entitled “Wavefront sensor for a staring imager”, U.S. Pat. No. 6,107,617 entitled “Liquid crystal active optics correction for large space based optical systems”, and the publication by R. Paxman, et al. entitled “Optical misalignment sensing and image reconstruction using phase diversity,” J. Opt. Soc. Am., A, 5, 914 (1988), each use phase diversity to estimate the wavefront. It is noted that the phase diversity approach to wavefront sensing was used to determine the aberration in the Hubble telescope project.
Note that all of the patents mentioned in the section on phase diversity use an in-focus image, an out-of-focus image, and a fixed diversity to perform wavefront sensing, as opposed to the current invention which uses sequential, in-focus images and sequential diversities which are the sequential changes in the adaptive optic device. The invention does not need additional equipment, such as an out-of-focus image, to control an adaptive optic device in the camera system.
One purpose of the instant invention is to provide a system for determining aberrations within a video camera or the optical medium and to eliminate the aberrations using no additional optics or sensors.